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href="/frontend/js%E5%9F%BA%E7%A1%80/%E4%BB%BB%E5%8A%A1%E7%AE%A1%E7%90%86.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>任务管理</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%87%BD%E6%95%B0%E8%BF%9B%E9%98%B6.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>函数进阶</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%8E%9F%E5%9E%8B%E4%B8%8E%E7%BB%A7%E6%89%BF.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>原型与继承</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%9F%BA%E6%9C%AC%E7%B1%BB%E5%9E%8B.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>基本类型</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%AF%B9%E8%B1%A1.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>对象</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%B8%B8%E7%94%A8%E6%8A%80%E5%B7%A7.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>常用技巧</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E6%95%B0%E7%BB%84%E7%B1%BB%E5%9E%8B.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>数组类型</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E6%A8%A1%E5%9D%97%E8%AE%BE%E8%AE%A1.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>模块设计</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E6%AD%A3%E5%88%99%E8%A1%A8%E8%BE%BE%E5%BC%8F.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>正则表达式</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E7%A9%BA%E9%97%B4%E5%9D%90%E6%A0%87.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>空间坐标</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E7%B1%BB.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>类</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-b7550ba0 data-v-b7550ba0><div class="item" data-v-b7550ba0><div class="indicator" data-v-b7550ba0></div><a class="VPLink link link" href="/frontend/js%E5%9F%BA%E7%A1%80/%E8%BF%AD%E4%BB%A3%E5%99%A8.html" data-v-b7550ba0><!--[--><p class="text" data-v-b7550ba0>迭代器</p><!--]--></a><!----></div><!----></div><!--]--></div></section></div><!--]--><!--[--><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-5d98c3a5 data-v-1428d186><div class="VPDoc has-sidebar has-aside" data-v-1428d186 data-v-39a288b8><!--[--><!--]--><div class="container" data-v-39a288b8><div class="aside" data-v-39a288b8><div class="aside-curtain" data-v-39a288b8></div><div class="aside-container" data-v-39a288b8><div class="aside-content" data-v-39a288b8><div class="VPDocAside" data-v-39a288b8 data-v-3f215769><!--[--><!--]--><!--[--><!--]--><nav aria-labelledby="doc-outline-aria-label" class="VPDocAsideOutline" data-v-3f215769 data-v-a5bbad30><div class="content" data-v-a5bbad30><div class="outline-marker" data-v-a5bbad30></div><div aria-level="2" class="outline-title" id="doc-outline-aria-label" role="heading" data-v-a5bbad30>目录</div><ul class="VPDocOutlineItem root" data-v-a5bbad30 data-v-b933a997><!--[--><!--]--></ul></div></nav><!--[--><!--]--><div class="spacer" data-v-3f215769></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-39a288b8><div class="content-container" data-v-39a288b8><!--[--><!--]--><main class="main" data-v-39a288b8><div style="position:relative;" class="vp-doc _frontend_js%E5%9F%BA%E7%A1%80_%E6%95%B0%E7%BB%84%E7%B1%BB%E5%9E%8B" data-v-39a288b8><div><h1 id="数组类型" tabindex="-1">数组类型 <a class="header-anchor" href="#数组类型" aria-label="Permalink to &quot;数组类型&quot;">​</a></h1><h3 id="array-from" tabindex="-1">Array.from <a class="header-anchor" href="#array-from" aria-label="Permalink to &quot;Array.from&quot;">​</a></h3><p>使用<code>Array.from</code>可将类数组转换为数组，类数组指包含 <code>length</code> 属性或可迭代的对象。</p><h4 id="类数组对象" tabindex="-1">类数组对象 <a class="header-anchor" href="#类数组对象" aria-label="Permalink to &quot;类数组对象&quot;">​</a></h4><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> str</span><span style="color:#56B6C2;"> =</span><span style="color:#98C379;"> &#39;我爱你&#39;</span><span style="color:#ABB2BF;">;</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">Array</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">from</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">str</span><span style="color:#ABB2BF;">)); </span><span style="color:#7F848E;font-style:italic;">//[&quot;我&quot;, &quot;爱&quot;, &quot;你&quot;]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>为对象设置<code>length</code>属性后也可以转换为数组，但要下标为数值或数值字符串，并且对象键值为数值或数值字符串。</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> user</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> {</span></span>
<span class="line"><span style="color:#98C379;">    &quot;name&quot;</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;love&#39;</span><span style="color:#ABB2BF;">,</span></span>
<span class="line"><span style="color:#98C379;">    &#39;1&#39;</span><span style="color:#ABB2BF;">: </span><span style="color:#D19A66;">18</span><span style="color:#ABB2BF;">,</span></span>
<span class="line"><span style="color:#E06C75;">    length</span><span style="color:#ABB2BF;">: </span><span style="color:#D19A66;">5</span></span>
<span class="line"><span style="color:#ABB2BF;">}</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">Array</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">from</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">user</span><span style="color:#ABB2BF;">)) </span><span style="color:#7F848E;font-style:italic;">//[undefined, 18, undefined, undefined, undefined]</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E06C75;">user</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> {</span></span>
<span class="line"><span style="color:#D19A66;">    1</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;1&#39;</span><span style="color:#ABB2BF;">,</span></span>
<span class="line"><span style="color:#98C379;">    &quot;2&quot;</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;love&#39;</span><span style="color:#ABB2BF;">,</span></span>
<span class="line"><span style="color:#98C379;">    &#39;4&#39;</span><span style="color:#ABB2BF;">: </span><span style="color:#D19A66;">18</span><span style="color:#ABB2BF;">,</span></span>
<span class="line"><span style="color:#E06C75;">    length</span><span style="color:#ABB2BF;">: </span><span style="color:#D19A66;">5</span></span>
<span class="line"><span style="color:#ABB2BF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">Array</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">from</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">user</span><span style="color:#ABB2BF;">)) </span><span style="color:#7F848E;font-style:italic;">// [undefined, &#39;1&#39;, &#39;love&#39;, undefined, 18]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><p>DOM 元素转换为数组后来使用数组函数，第二个参数类似于<code>map</code> 函数的方法，可对数组元素执行函数处理。</p><div class="language-html line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">html</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#ABB2BF;">&lt;</span><span style="color:#E06C75;">body</span><span style="color:#ABB2BF;">&gt;</span></span>
<span class="line"><span style="color:#ABB2BF;">    &lt;</span><span style="color:#E06C75;">button</span><span style="color:#D19A66;"> message</span><span style="color:#ABB2BF;">=</span><span style="color:#98C379;">&quot;button1&quot;</span><span style="color:#ABB2BF;">&gt;button&lt;/</span><span style="color:#E06C75;">button</span><span style="color:#ABB2BF;">&gt;</span></span>
<span class="line"><span style="color:#ABB2BF;">    &lt;</span><span style="color:#E06C75;">button</span><span style="color:#D19A66;"> message</span><span style="color:#ABB2BF;">=</span><span style="color:#98C379;">&quot;button2&quot;</span><span style="color:#ABB2BF;">&gt;button&lt;/</span><span style="color:#E06C75;">button</span><span style="color:#ABB2BF;">&gt;</span></span>
<span class="line"><span style="color:#ABB2BF;">&lt;/</span><span style="color:#E06C75;">body</span><span style="color:#ABB2BF;">&gt;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#ABB2BF;">&lt;</span><span style="color:#E06C75;">script</span><span style="color:#ABB2BF;">&gt;</span></span>
<span class="line"><span style="color:#C678DD;">    let</span><span style="color:#E06C75;"> btns</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> document</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">querySelectorAll</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">&#39;button&#39;</span><span style="color:#ABB2BF;">);</span></span>
<span class="line"><span style="color:#E5C07B;">    console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">btns</span><span style="color:#ABB2BF;">); </span><span style="color:#7F848E;font-style:italic;">//包含length属性</span></span>
<span class="line"><span style="color:#E5C07B;">    Array</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">from</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">btns</span><span style="color:#ABB2BF;">, (</span><span style="color:#E06C75;font-style:italic;">item</span><span style="color:#ABB2BF;">) </span><span style="color:#C678DD;">=&gt;</span><span style="color:#ABB2BF;"> {</span></span>
<span class="line"><span style="color:#E5C07B;">        item</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">style</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">background</span><span style="color:#56B6C2;"> =</span><span style="color:#98C379;"> &#39;red&#39;</span><span style="color:#ABB2BF;">;</span></span>
<span class="line"><span style="color:#ABB2BF;">    });</span></span>
<span class="line"><span style="color:#ABB2BF;">&lt;/</span><span style="color:#E06C75;">script</span><span style="color:#ABB2BF;">&gt;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><h2 id="解构赋值" tabindex="-1">解构赋值 <a class="header-anchor" href="#解构赋值" aria-label="Permalink to &quot;解构赋值&quot;">​</a></h2><h3 id="默认值" tabindex="-1">默认值 <a class="header-anchor" href="#默认值" aria-label="Permalink to &quot;默认值&quot;">​</a></h3><p>为变量设置默认值</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#ABB2BF;"> [</span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">, </span><span style="color:#E06C75;">site</span><span style="color:#56B6C2;"> =</span><span style="color:#98C379;"> &#39;v1&#39;</span><span style="color:#ABB2BF;">] </span><span style="color:#56B6C2;">=</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&#39;v2&#39;</span><span style="color:#ABB2BF;">];</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">site</span><span style="color:#ABB2BF;">); </span><span style="color:#7F848E;font-style:italic;">//v1</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="扩展语法" tabindex="-1">扩展语法 <a class="header-anchor" href="#扩展语法" aria-label="Permalink to &quot;扩展语法&quot;">​</a></h3><p>使用<code>fill</code> 填充数组元素</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#E5C07B;">  console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">dir</span><span style="color:#ABB2BF;">(</span><span style="color:#61AFEF;">Array</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">4</span><span style="color:#ABB2BF;">).</span><span style="color:#61AFEF;">fill</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">&quot;love&quot;</span><span style="color:#ABB2BF;">));</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>指定填充位置</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">([</span><span style="color:#D19A66;">1</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">2</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">3</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">4</span><span style="color:#ABB2BF;">].</span><span style="color:#61AFEF;">fill</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">&quot;love&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">1</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">2</span><span style="color:#ABB2BF;">)); </span><span style="color:#7F848E;font-style:italic;">//[1, &quot;love&quot;, 3, 4]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><h3 id="splice" tabindex="-1">splice <a class="header-anchor" href="#splice" aria-label="Permalink to &quot;splice&quot;">​</a></h3><p>删除数组元素第一个参数为从哪开始删除，第二个参数为删除的数量。</p><p>通过修改<code>length</code>删除最后一个元素</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> arr</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&quot;love&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;you&quot;</span><span style="color:#ABB2BF;">];</span></span>
<span class="line"><span style="color:#E5C07B;">arr</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">length</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> arr</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">length</span><span style="color:#56B6C2;"> -</span><span style="color:#D19A66;"> 1</span><span style="color:#ABB2BF;">;</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">arr</span><span style="color:#ABB2BF;">) </span><span style="color:#7F848E;font-style:italic;">// [love]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h3 id="copywithin" tabindex="-1">copyWithin <a class="header-anchor" href="#copywithin" aria-label="Permalink to &quot;copyWithin&quot;">​</a></h3><p>使用 <code>copyWithin</code> 从数组中复制一部分到同数组中的另外位置。</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> arr</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#D19A66;">1</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">2</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">3</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">4</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">5</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">6</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">7</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">8</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">9</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">]</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">arr</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">copyWithin</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">4</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">7</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">9</span><span style="color:#ABB2BF;">)) </span><span style="color:#7F848E;font-style:italic;">//[1, 2, 3, 4, 8, 9, 7, 8, 9, 10]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h2 id="查找元素" tabindex="-1">查找元素 <a class="header-anchor" href="#查找元素" aria-label="Permalink to &quot;查找元素&quot;">​</a></h2><h3 id="find" tabindex="-1">find <a class="header-anchor" href="#find" aria-label="Permalink to &quot;find&quot;">​</a></h3><p>find 方法找到后会把值返回出来，参数为函数.</p><ul><li>如果找不到返回值为<code>undefined</code></li></ul><p>返回第一次找到的值，不继续查找</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> arr</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&quot;1&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;2&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;3&quot;</span><span style="color:#ABB2BF;">]</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">arr</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">find</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;font-style:italic;">item</span><span style="color:#C678DD;"> =&gt;</span><span style="color:#E06C75;"> item</span><span style="color:#56B6C2;"> ==</span><span style="color:#98C379;"> &quot;3&quot;</span><span style="color:#ABB2BF;">)) </span><span style="color:#7F848E;font-style:italic;">// 3</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>使用<code>includes</code>等不能查找引用类型，因为它们的内存地址是不相等的</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> user</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [{ </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;1&quot;</span><span style="color:#ABB2BF;"> }, { </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;2&quot;</span><span style="color:#ABB2BF;"> }, { </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;3&quot;</span><span style="color:#ABB2BF;"> }]</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">user</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">includes</span><span style="color:#ABB2BF;">({ </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;3&quot;</span><span style="color:#ABB2BF;"> })) </span><span style="color:#7F848E;font-style:italic;">//false</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><code>find</code> 可以方便的查找引用类型</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> user</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [{ </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;1&quot;</span><span style="color:#ABB2BF;"> }, { </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;2&quot;</span><span style="color:#ABB2BF;"> }, { </span><span style="color:#E06C75;">name</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&quot;3&quot;</span><span style="color:#ABB2BF;"> }]</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">user</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">find</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;font-style:italic;">user</span><span style="color:#C678DD;"> =&gt;</span><span style="color:#ABB2BF;"> (</span><span style="color:#E5C07B;">user</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">name</span><span style="color:#56B6C2;"> =</span><span style="color:#98C379;"> &quot;3&quot;</span><span style="color:#ABB2BF;">))) </span><span style="color:#7F848E;font-style:italic;">//{name: &#39;3&#39;}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h2 id="循环遍历" tabindex="-1">循环遍历 <a class="header-anchor" href="#循环遍历" aria-label="Permalink to &quot;循环遍历&quot;">​</a></h2><h3 id="foreach" tabindex="-1">forEach <a class="header-anchor" href="#foreach" aria-label="Permalink to &quot;forEach&quot;">​</a></h3><p><code>forEach</code>使函数作用在每个数组元素上，但是没有返回值。</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> lessons</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span></span>
<span class="line"><span style="color:#ABB2BF;">  {</span><span style="color:#E06C75;">title</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;媒体查询响应式布局&#39;</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">category</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;css&#39;</span><span style="color:#ABB2BF;">},</span></span>
<span class="line"><span style="color:#ABB2BF;">  {</span><span style="color:#E06C75;">title</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;FLEX 弹性盒模型&#39;</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">category</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;css&#39;</span><span style="color:#ABB2BF;">},</span></span>
<span class="line"><span style="color:#ABB2BF;">  {</span><span style="color:#E06C75;">title</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;MYSQL多表查询随意操作&#39;</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">category</span><span style="color:#ABB2BF;">: </span><span style="color:#98C379;">&#39;mysql&#39;</span><span style="color:#ABB2BF;">}</span></span>
<span class="line"><span style="color:#ABB2BF;">];</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E5C07B;">lessons</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">forEach</span><span style="color:#ABB2BF;">((</span><span style="color:#E06C75;font-style:italic;">item</span><span style="color:#ABB2BF;">, </span><span style="color:#E06C75;font-style:italic;">index</span><span style="color:#ABB2BF;">, </span><span style="color:#E06C75;font-style:italic;">array</span><span style="color:#ABB2BF;">) </span><span style="color:#C678DD;">=&gt;</span><span style="color:#ABB2BF;"> {</span></span>
<span class="line"><span style="color:#E5C07B;">    item</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">title</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> item</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">title</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">substr</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">0</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">5</span><span style="color:#ABB2BF;">);</span></span>
<span class="line"><span style="color:#ABB2BF;">});</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">lessons</span><span style="color:#ABB2BF;">);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><h3 id="for-in" tabindex="-1">for/in <a class="header-anchor" href="#for-in" aria-label="Permalink to &quot;for/in&quot;">​</a></h3><p>遍历时的 key 值为数组的索引</p><h3 id="for-of" tabindex="-1">for/of <a class="header-anchor" href="#for-of" aria-label="Permalink to &quot;for/of&quot;">​</a></h3><p>与 <code>for/in</code> 不同的是 <code>for/of</code> 每次循环取其中的值而不是索引。尤其用于迭代器方法。</p><h2 id="迭代器方法" tabindex="-1">迭代器方法 <a class="header-anchor" href="#迭代器方法" aria-label="Permalink to &quot;迭代器方法&quot;">​</a></h2><h3 id="keys" tabindex="-1">keys <a class="header-anchor" href="#keys" aria-label="Permalink to &quot;keys&quot;">​</a></h3><p>通过迭代对象获取索引</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> arr</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&quot;a&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;b&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;c&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;d&quot;</span><span style="color:#ABB2BF;">]</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C678DD;">for</span><span style="color:#ABB2BF;"> (</span><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> key</span><span style="color:#C678DD;"> of</span><span style="color:#E5C07B;"> arr</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">keys</span><span style="color:#ABB2BF;">()) {</span></span>
<span class="line"><span style="color:#E5C07B;">    console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">key</span><span style="color:#ABB2BF;">)</span></span>
<span class="line"><span style="color:#ABB2BF;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>使用 while 遍历，注意死循环控制。</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> arr</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&quot;I&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;love&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;you&quot;</span><span style="color:#ABB2BF;">]</span></span>
<span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> keys</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> arr</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">keys</span><span style="color:#ABB2BF;">()</span></span>
<span class="line"><span style="color:#C678DD;">let</span><span style="color:#E06C75;"> key</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> keys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">next</span><span style="color:#ABB2BF;">()</span></span>
<span class="line"><span style="color:#C678DD;">while</span><span style="color:#ABB2BF;"> (</span><span style="color:#56B6C2;">!</span><span style="color:#E5C07B;">key</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">done</span><span style="color:#ABB2BF;">) {</span></span>
<span class="line"><span style="color:#E5C07B;">    console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">key</span><span style="color:#ABB2BF;">.</span><span style="color:#E06C75;">value</span><span style="color:#ABB2BF;">)</span></span>
<span class="line"><span style="color:#E06C75;">    key</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> keys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">next</span><span style="color:#ABB2BF;">()</span></span>
<span class="line"><span style="color:#ABB2BF;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><h2 id="values" tabindex="-1">values <a class="header-anchor" href="#values" aria-label="Permalink to &quot;values&quot;">​</a></h2><p>通过迭代对象获取值</p><h3 id="entries" tabindex="-1">entries <a class="header-anchor" href="#entries" aria-label="Permalink to &quot;entries&quot;">​</a></h3><p>返回数组所有键值对，下面使用解构语法循环</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki one-dark-pro vp-code" style="background-color:#282c34;color:#abb2bf;" tabindex="0"><code><span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> hd</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> [</span><span style="color:#98C379;">&quot;love&quot;</span><span style="color:#ABB2BF;">, </span><span style="color:#98C379;">&quot;u&quot;</span><span style="color:#ABB2BF;">]</span></span>
<span class="line"><span style="color:#C678DD;">const</span><span style="color:#E5C07B;"> iterator</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> hd</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">entries</span><span style="color:#ABB2BF;">()</span></span>
<span class="line"><span style="color:#C678DD;">let</span><span style="color:#ABB2BF;"> { </span><span style="color:#E06C75;">done</span><span style="color:#ABB2BF;">, </span><span style="color:#E06C75;">value</span><span style="color:#ABB2BF;">: [</span><span style="color:#E06C75;">k</span><span style="color:#ABB2BF;">, </span><span style="color:#E06C75;">v</span><span style="color:#ABB2BF;">] } </span><span style="color:#56B6C2;">=</span><span style="color:#E5C07B;"> iterator</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">next</span><span style="color:#ABB2BF;">()</span></span>
<span class="line"><span style="color:#E5C07B;">console</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">log</span><span style="color:#ABB2BF;">(</span><span style="color:#E06C75;">v</span><span style="color:#ABB2BF;">);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><h2 id="扩展方法" tabindex="-1">扩展方法 <a class="header-anchor" href="#扩展方法" aria-label="Permalink to &quot;扩展方法&quot;">​</a></h2><h3 id="every" tabindex="-1">every <a class="header-anchor" href="#every" aria-label="Permalink to &quot;every&quot;">​</a></h3><p><code>every</code> 用于递归的检测元素，要所有元素操作都要返回真结果才为真。</p><h3 id="some" tabindex="-1">some <a class="header-anchor" href="#some" aria-label="Permalink to &quot;some&quot;">​</a></h3><p>使用 <code>some</code> 函数可以递归的检测元素，如果有一个返回 true，表达式结果就是真。</p><h3 id="reduce" tabindex="-1">reduce <a class="header-anchor" href="#reduce" aria-label="Permalink to &quot;reduce&quot;">​</a></h3><p>使用 <code>reduce</code> 与 <code>reduceRight</code> 函数可以迭代数组的所有元素，<code>reduce</code> 从前开始 <code>reduceRight</code> 从后面开始。下面通过函数计算课程点击数的和。</p><p>第一个参数是执行函数，第二个参数为初始值</p><ul><li>传入第二个参数时将所有元素循环一遍</li><li>不传第二个参数时从第二个元素开始循环</li></ul><p>函数参数说明如下</p><table tabindex="0"><thead><tr><th>参数</th><th>说明</th></tr></thead><tbody><tr><td>prev</td><td>上次调用回调函数返回的结果</td></tr><tr><td>cur</td><td>当前的元素值</td></tr><tr><td>index</td><td>当前的索引</td></tr><tr><td>array</td><td>原数组</td></tr></tbody></table></div></div></main><footer class="VPDocFooter" data-v-39a288b8 data-v-e257564d><!--[--><!--]--><div class="edit-info" data-v-e257564d><!----><div class="last-updated" data-v-e257564d><p class="VPLastUpdated" data-v-e257564d data-v-e98dd255>最后更新: <time datetime="2024-12-30T14:20:32.000Z" data-v-e98dd255></time></p></div></div><nav class="prev-next" aria-labelledby="doc-footer-aria-label" data-v-e257564d><span class="visually-hidden" id="doc-footer-aria-label" data-v-e257564d>Pager</span><div class="pager" data-v-e257564d><a class="VPLink link pager-link prev" href="/frontend/js%E5%9F%BA%E7%A1%80/%E5%B8%B8%E7%94%A8%E6%8A%80%E5%B7%A7.html" data-v-e257564d><!--[--><span class="desc" data-v-e257564d>上一篇</span><span class="title" data-v-e257564d>常用技巧</span><!--]--></a></div><div class="pager" data-v-e257564d><a class="VPLink link pager-link next" href="/frontend/js%E5%9F%BA%E7%A1%80/%E6%A8%A1%E5%9D%97%E8%AE%BE%E8%AE%A1.html" data-v-e257564d><!--[--><span class="desc" data-v-e257564d>下一篇</span><span class="title" data-v-e257564d>模块设计</span><!--]--></a></div></nav></footer><!--[--><!--]--></div></div></div><!--[--><!--]--></div></div><!----><!--[--><!--]--></div></div>
    
    
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